The invention relates to telecommunications systems and particularly to an arrangement for passing a message to a user terminal located in a shadow region in a telecommunications system based on a radio connection.
Mobile systems enable subscribers to move within the working range of a network so that they remain within the reach of teleservices. The working range of a mobile system consists of cells provided by base stations. A mobile station functioning as a user terminal, a radio system comprising base stations and base station controllers that control them, and a system of mobile switching centres monitor the movements of a subscriber so that the subscriber can move freely from one cell in the working range to another without needing to know in the area of which cell he currently is.
However, matters affecting propagation of radio waves, such as attenuation, reflection, etc., provide shadow regions in the working range; in shadow regions, the network connection weakens significantly or disappears altogether. A shadow region may result from a temporary obstacle in the propagation direction of a radio wave or from a permanent obstacle, such as a steep wall or a multi-storey building, stopping the propagation of the radio waves. Shadow regions are problematic to all telecommunication on the radio path.
The problem becomes particularly apparent in satellite mobile systems, in which the whole globe can be covered by a rather small number of satellites thanks to the large cell size. Because of the frequencies and transmission powers used, however, a satellite mobile system in practice covers only outdoor areas; in other words, when a user moves inside or e.g. under a roof, the network connection weakens significantly or disappears altogether. This greatly impairs the operability of a satellite mobile system.
The GSM system (Global System for Mobile Communications) comprises a Short Message Service SMS facilitating the reaching of a subscriber: a message to a subscriber that is not reached can be forwarded to the user terminal in packet form immediately as the system detects that the subscriber can be reached. A short message can be supplied to a subscriber always when the subscriber is registered in the network, i.e. even when the subscriber is participating in a call. A short message is usually associated with conditional call forwarding and a voice message so that if a call to a subscriber cannot be successfully set up, the calling party can leave a voice message for the subscriber concerned. The storage of a voice message in the system generates a short message from the short message service centre, whereby the subscriber is notified in the above manner of the call attempt immediately as he registers in the network.
Successful forwarding of a short message, however, also requires a network connection with the user terminal. A subscriber located in a shadow region cannot thus receive information indicating whether the system has attempted to reach him. An essential improvement in the reachability of a subscriber in mobile systems would be a paging message type notification that would reach the subscriber that the mobile system is attempting to reach in a shadow region, for example in connection with call set-up.
The object of the present invention is to provide a service that significantly improves the possibility of supplying a message to a user terminal when the subscriber is located in a shadow region. The aim of the service is that after receiving the message, the subscriber canxe2x80x94is he so desiresxe2x80x94move to an area where the network connection is better or he can attempt to receive the message in some other way. In particular, the invention provides a network level solution to forwarding a message to a subscriber in a mobile system. The probability of the data reaching the destination is called penetration capacity.
The invention is characterized in that the arrangement comprises at least one high penetration paging channel, the penetration capacity of a transmission on the channel being arranged to be essentially higher than on the other channels of the telecommunications system; and equipment, responsive to a failed attempt to reach the user terminal on a normal paging channel of the telecommunications system, for issuing and transmitting a message with high penetration capacity on said at least one high penetration paging channel.
The invention also relates to a user terminal which is characterized in that the user terminal, in response to moving to a shadow region, starts to listen to a paging channel allocated for transmission of a paging message with high penetration capacity, and that the user terminal, in response to reception of the high penetration paging message, indicates the reception of said message by indicators arranged in the user terminal.
The invention also relates to a method of supplying a message to a user terminal located in a shadow region in a telecommunications system based on a radio connection. The method is characterized by comprising the steps of unsuccessfully paging the user terminal on a normal paging channel of the telecommunications system, and sending said user terminal a high penetration message on at least one high penetration paging channel, the penetration capacity of a transmission on the channel being much higher than on the other channels of the telecommunications system.
The invention is based on the idea of arranging in the mobile system at least one channel which gives the signal burst transmitted a better chance of reaching the user terminal despite attenuation. When the user terminal detects that it is in a shadow region, it proceeds to listen to a channel allocated for a high penetration paging message. When the system attempts to reach a subscriber but the attempts by normal network arrangements are unsuccessful, a high penetration paging message is issued and transmitted to the subscriber on said channel. After receiving the message, the subscriber can move away from the shadow region and contact the system.
To implement the service, a separate service centre associated with a high penetration paging message is added to the mobile system, the service centre being essentially an administrative database. When the paging of a subscriber is unsuccessful, the functional unit of the mobile system responsible for call set-up and mobility management, e.g. a mobile exchange, forwards information about the failed paging to the service centre. In the service centre is issued a paging message, and the message is forwarded by a high penetration signal burst to the user terminal in the system.
Indication of a call attempt to a subscriber located in a shadow region is a major problem in all telecommunication on the radio path. The present invention is suitable for use in analogue and digital mobile networks and in packet systems. It significantly improves the reachability of a subscriber in a mobile system and thereby essentially improves the known technology. In addition, an improvement in the reachability of user terminals also makes them more useful as paging devices, so that the subscriber does not necessarily need two separate devices: one for paging and the other for telephone services. The solution of the invention is suitable for use in all telecommunications networks based on a radio connection.